The present invention relates to a compact helical compressor for mobile use in a motor vehicle including a helical compressor unit which is driven by a motor unit.
In vehicle technology, helical compressors are used wherever, despite restricted space being available, compressed air has to be generated in order to supply a compressed air on-board system. The design principle of a helical compressor is inherently suitable for a particularly compact design, and is described, for example, in German patent document DE 34 22 398.
From the general prior art it is known that the helical compressors which are used in vehicles, such as commercial or utility vehicles or rail vehicles, are driven by the drive assembly of the vehicle, for example by a diesel engine. This can be done by directly coupling a helical compressor unit to this motor unit as is described, for example, in U.S. Pat. No. 3,811,805. Alternatively, it is also possible to provide a transmission with a fixed transmission ratio between the drive assembly of the vehicle, i.e. the motor unit, and the helical compressor unit. Such a transmission usually includes a V-belt transmission.
A disadvantage of this conventional design is that the discharge rate of compressed air which is generated by the helical compressor unit is dependent on the rotational speed of the drive assembly of the vehicle. Therefore, the discharge rate of the helical compressor unit drops when the drive assembly rotates less quickly, that is to say for example if the vehicle is braked. Conversely, the discharge rate of the helical compressor unit rises with a rising rotational speed of the drive assembly, for example if the vehicle is accelerated. As a result of this, it is possible to encounter the problem that at operating points at which there is a high demand for compressed air for the vehicle (for example when braking) only a low output rotational speed of the drive assembly is available for generating a corresponding discharge volume of compressed air, and it is not possible to ensure that compressed air is provided in accordance with demand.
In order to solve this problem, attempts have previously been made to equip the compressed air system of a vehicle with sufficiently large storage containers for compressed air, from which the necessary compressed air is made available at demand peaks. However, this solution has the disadvantage that such compressed air containers require a correspondingly large installation volume in the vehicle, which runs counter to the objective of a compressed air system which is as compact overall as possible.
The present invention provides a compact helical compressor for mobile use in a vehicle whose discharge rate of compressed air is largely independent of the fluctuating rotational speed of the drive assembly.
In one exemplary embodiment, a compact mobile helical compressor is provided, driven by a dedicated motor unit assigned solely to the compressor, to generate a discharge rate of compressed air independent of the vehicle drive assembly. The subsequent specification and claims will describe additional embodiments of the invention.
The invention in one exemplary embodiment describes that the rotational speed of the motor unit, which is assigned solely to the helical compressor unit, can be adjusted in accordance with a control unit in such a way that the helical compressor unit generates a predefined discharge rate of compressed air independently of the drive assembly of the vehicle.
The advantage of the drive of the helical compressor which, according to an exemplary embodiment of the invention, can be controlled in accordance with demand is that even at operating points at which there is a high demand for compressed air but with only a low output rotational speed of the drive assembly of the vehicle being available, a sufficient discharge rate of compressed air can be generated. It is thus possible to dispense with additional large compressed air containers.
By using the control unit according to the invention, it is possible to adjust the discharge rate, and thus the power consumption of the helical compressor according to the invention precisely to the requirements of a suitable motor unit, and to adapt to changing requirements during operation at any time without further retrofitting of mechanical components, as is necessary, for example, when changing over the use of buses in public transport between town center mode and suburban mode.
The motor unit which exclusively drives the helical compressor unit can be embodied in the manner of a hydraulic drive or in the manner of an electric motor. The decisive factor in the selection of the motor unit within the scope of the present invention is that it is suitable as an actuator element within the scope of the demand-oriented rotational speed controller described here.
The use of the controllable hydraulic drive permits energy-saving deactivation of the helical compressor according to the invention, without necessitating coupling elements which are subject to wear, merely by changing the pivot angle on the hydraulic pump of the hydraulic drive, initiated by the control unit.
The controllable hydraulic drive is preferably composed of a hydraulic motor which is connected directly by flanges to the helical compressor unit and which an adjustable hydraulic pump supplies with pressure medium necessary for operation, wherein the adjustable hydraulic pump is actuated by the control unit. As an alternative to the noncontrollable hydraulic motor on the helical compressor unit, it is possible also to provide a controllable hydraulic motor if a continuously present circuit is available.
Furthermore, it is also alternatively envisioned to replace the hydraulic motor by an electric motor. An electric motor may, for example, be preferably used as a motor unit if the vehicle is embodied in the manner of a hybrid vehicle. In such a hybrid vehicle, the drive of the vehicle is primarily provided by an electric motor for which electric current is generated by a generator which is driven by a diesel engine. Excess electric current can be fed into a battery here. In such a hybrid vehicle electric current is therefore present in any case in order also to supply the separate electric motor of the helical compressor with the necessary operating energy. The separate electric motor is preferably embodied as a three-phase motor which receives its operating energy via a power inverter from the DC voltage generated by the generator.
According to a further exemplary embodiment according to the invention, the helical compressor unit includes preferably three housing parts which are connected to one another without external lines by mounting them one next to the other, so that together they form the helical compressor unit. The housing parts are preferably embodied from cast metal. Within the housing parts it is possible to accommodate numerous functions in a space-saving fashion. Furthermore, this design eliminates all the external piping of the compressor functions.
A first housing part of the exemplary multi-component housing advantageously includes at least one intake nonreturn valve with a compressor helical arrangement connected downstream, with an oil pre-separator unit connected downstream, containing an oil sump with a slosh preventer, with a pressure relief unit connected downstream (for use when the unit is switched off). All these functional parts of the helical compressor unit can be efficiently integrated in a first, common housing part.
In a second housing part which is assigned or connected to the first housing part, the outflow contour of the helical compressor unit is preferably formed together with elements for returning oil from the oil sump, at least one oil filter with an optional oil thermostat and at least one oil inflow connector.
With the aforementioned two housing parts it is advantageously possible to combine a third housing part which preferably contains elements for accommodating a fine oil filter, elements for extracting oil, pressure holding valve elements and nonreturn valve elements.
In the helical compressor unit, which is preferably composed of the three abovementioned housing parts with respectively integrated components, it is possible to dispense with all the external and internal piping which is otherwise customary, in particular for relieving pressure when switching off, for returning oil from the fine precipitator, etc.
According to a further exemplary embodiment which improves the invention, there is a provision for the hydraulic motor to be coupled by a driver disk to the helical compressor unit in which the shaft ends of the hydraulic motor and helical compressor unit engage. The driver disk is damped and lubricated by an oil circuit or a continuous grease lubrication component. Using a damped driver disk of this type ensures particularly wear-free coupling of the hydraulic motor to the helical compressor unit. For this purpose, elastic couplings or rigid couplings are generally used provided there is no speed-changing drive via V-belts or a transmission. These coupling elements are subject to wear and permit only a rigid connection between the assembly containing the hydraulic motor and the assembly containing the helical compressor unit.
According to another exemplary embodiment which improves the invention, the oil circuit, which is necessary to cool the helical compressor unit, can be coupled via a heat exchanger to a thermostatically controlled cooling circuit of the vehicle. This measure allows a separate temperature control of the oil circuit for cooling the helical compressor unit to be entirely dispensed with. As a cooling circuit of the vehicle it is possible to use the cooling circuit for lubricating the vehicle shaft, differential, etc. or the engine cooling circuit. This also makes it possible to connect the heat exchanger directly to the helical compressor unit or alternatively to the drive assembly of the vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.